We propose to continue our previous investigations on the nature and function of the mammalian phospholipase. Specifically we plan to: 1) Lysosomes - The lysosomal enzymes will be purified to homogeneity and its role in the breakdown of the lysosomal membrane studied. Compounds known to stabilize the lysosomal membrane will be used to determine the role of the phospholipases in disruption of the lysosome. 2) Plasma Membranes - Lipoproteins will be labeled with glycerides and phospholipids which will be used as substrate for the solubilized phospholipase A1 from plasma membranes. Isolated liver cells will be used to study the role of the phospholipase A1 in liver uptake of lipids from lipoproteins. Also, the enzyme purified from the serum will be studied in collaboration with Dr. F. Zieve to demonstrate that one enzyme (or show that more than one enzyme) is responsible for the hydrolytic and transacylation activities. 3) Hepatomas - Selected highly differentiated and poorly differentiated hepatomas will be obtained from rats provided by Dr. Morris's group at Howard University. These will be compared with normal liver and livers from host animals for altered lipid composition of the membranes and for changes in phospholipase activity.